2 Chemical Reactive Hazard CBE 465Chemical Reactive Hazard4/12/2017Chemical reactivity hazard: situation with potential for an uncontrolled chemical reaction, resulting in harm to people, equipment, or environment.Result could be:Violent release of heat, toxic or flammable materialsBuild up of excessive pressureReaction could be:Self-reacting chemical (i.e., monomer)With other chemicals; intentional or otherwiseCatalyzed by contamination, construction materialsExothermic and/or gas producingDue to incompatibility
3 Screening for Reactive Hazards CBE 465Screening for Reactive Hazards4/12/2017Figure 8-1 Screening flowchart for reactive chemical hazards. An answer of “yes” at any decision point moves more toward reactive chemisty. See Section 8.2 for more details. (Source: R.W Johnson, S.W. Rudy, and S. D. Unwin, Essential Practices for Managing Chemical Reactivity Hazards (New York: AIChE Center for Chemical Process Safety, 2003.))
4 Specific Chemical Reactive Hazard CBE 465Specific Chemical Reactive Hazard4/12/2017
5 Specific Chemical Reactive Hazard CBE 465Specific Chemical Reactive Hazard4/12/2017
6 Specific Chemical Reactive Hazard CBE 465Specific Chemical Reactive Hazard4/12/2017
7 Specific Chemical Reactive Hazard CBE 465Specific Chemical Reactive Hazard4/12/2017Table AF-1: A few pyrophoric and spontaneously combustible categories and chemicals (these materials combust on exposure to air).Table AF-2: Some chemical structures susceptible to peroxide formation (the peroxides formed may become unstable and explode when disturbed).Table AF-3: Chemical categories susceptible to water reactivity.Table AF-4: Common water-reactive chemicals.Table AF-5: Typical oxidizers.Table AF-6: Some polymerizing compounds (these chemicals may polymerize rapidly with release of large amounts of heat).
8 Reactive Functional Groups CBE 465Reactive Functional Groups4/12/2017
9 Sources of Information CBE 465Sources of Information4/12/2017
10 Understanding Reactive Systems CBE 465Understanding Reactive Systems4/12/2017Cooling WaterExothermic ReactionRunaway reactions can occur whenever exothermic chemistry is used.Why important: Common problem with exothermic reactions.
11 Understanding Reactive Systems CBE 465Understanding Reactive Systems4/12/2017
12 Runaway Reactions How? 1. Loss of coolant. 2. Increased temperature. CBE 465Runaway Reactions4/12/2017How?1. Loss of coolant.2. Increased temperature.3. Increased energy generation.High pressure due to: Vapor pressure of liquid.Vapor decomposition products.Larger vessels respond faster - less heat transfer thru walls!!!Some chemicals can achieve self heat rates of 100’s deg. C/min! Styrene, Acrylic AcidThere are lots of ways for runaway reactions to occur. People somehow do not realize that a larger vessel will runaway faster since it has a lower surface to volume ratio with less heat losses.
13 Runaway Reactions Some ways for runaways to occur: Loss of cooling. CBE 465Runaway Reactions4/12/2017Some ways for runaways to occur:Loss of cooling.Overcharge reactant.External fire.Mis-charge reactant.Low reaction temperature in semi-batch reactor. This is called a sleeping reactor.Loss of agitation.Some ways for this to occur. Two phase flow is a very challenging engineering problem.Most reactive runaways result in 2-phase flow thru relief and require a relief area 2 to 10 times larger than single phase relief.
14 Understanding Reactive Systems CBE 465Understanding Reactive Systems4/12/2017
15 Application of Calorimeter Data CBE 465Application of Calorimeter Data4/12/2017Heat exchanger duty to achieve required reactor coolingCooling water requirements and cooling water pump sizeCondenser size in a reactor reflux systemMax conc. Of reactants to prevent overpressure in the reactorReactor vessel size and pressure ratingType of reactor (batch, semi-batch, tubular)Reactor temperature control and sequencingSemi-batch reactor reactant feed ratesCatalyst concentrations; max fill for batch and semi-batch reactorsAlarm/shutdown setpointsOperating and emergency proceduresRelief sizing and effluent treatment systemsSolvent concentrations required to control reactor temperaturePage 415 C&L 3rd ed.
19 CBE 465In-Class Exercise4/12/2017A company had a spray painting operation to paint automotive parts. The spray painting was done in a paint booth to reduce worker’s exposure and to collect any paint droplets that might be entrained in the exhaust air. The paint droplets were collected by fibrous filters. At the end of each day, the filters were removed, placed in plastic bags, and stored for disposal in a separate building.Due to environmental concerns over volatile emissions from paint solvents, the paint supplier reformulated the paint to use a less volatile solvent. This change was done in consultation with the paint company. Several test were done to ensure the reformulated paint worked well with the existing spray equipment and that the quality was satisfactory.The company switched to the reformulated paint. Several days later the disposal building caught on fire, apparently due to a fire started by the paint filters. Can you explain how this might have happened. Any suggestions for prevention?
20 CBE 465In-Class Exercise4/12/2017A university lab expansion includes installation of a distribution system to provide gaseous oxygen from manifolded cylinders to a biochemical engineering laboratory. No chemical reactivity hazards have been previously identified for the lab facilities.Apply the screening method of Figure 8-1 to determine if any chemical reactivity hazards are expected.
21 Runaway Reactions - 4 CBE 465 4/12/2017 A picture from the 1940s showing a relief discharge thru the roof of a building.